U.S. patent number 8,878,136 [Application Number 13/266,328] was granted by the patent office on 2014-11-04 for radiometric measuring device.
This patent grant is currently assigned to Endress + Hauser GmbH + Co. KG. The grantee listed for this patent is Hartmut Damm, Robert Schauble, Simon Weidenbruch. Invention is credited to Hartmut Damm, Robert Schauble, Simon Weidenbruch.
United States Patent |
8,878,136 |
Weidenbruch , et
al. |
November 4, 2014 |
Radiometric measuring device
Abstract
A radiometric measuring device comprising: a radioactive
radiator which sends radioactive radiation through a container; and
a detector serving to receive a radiation intensity penetrating
through the container, dependent on the physical, measured
variable, and to convert such into an electrical output signal. The
detector includes a carrier, on which at least one scintillation
fiber is wound, which converts radiometric radiation impinging
thereon into light flashes, whose light propagates in the
respective scintillation fiber toward its ends. The detector
further includes at least one array of avalanche photodiodes
operated in a Geiger mode, which convert light impinging thereon
into an electrical signal. The detector also has a measuring device
electronics connected to the avalanche photodiodes for producing
the electrical output signal, based on the electrical signals of
the avalanche photodiodes.
Inventors: |
Weidenbruch; Simon (Lorrach,
DE), Damm; Hartmut (Teningen, DE),
Schauble; Robert (Herrischried, DE) |
Applicant: |
Name |
City |
State |
Country |
Type |
Weidenbruch; Simon
Damm; Hartmut
Schauble; Robert |
Lorrach
Teningen
Herrischried |
N/A
N/A
N/A |
DE
DE
DE |
|
|
Assignee: |
Endress + Hauser GmbH + Co. KG
(Maulburg, DE)
|
Family
ID: |
42320719 |
Appl.
No.: |
13/266,328 |
Filed: |
April 8, 2010 |
PCT
Filed: |
April 08, 2010 |
PCT No.: |
PCT/EP2010/054653 |
371(c)(1),(2),(4) Date: |
October 26, 2011 |
PCT
Pub. No.: |
WO2010/127920 |
PCT
Pub. Date: |
November 11, 2010 |
Prior Publication Data
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|
|
Document
Identifier |
Publication Date |
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US 20120043466 A1 |
Feb 23, 2012 |
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Foreign Application Priority Data
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|
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May 5, 2009 [DE] |
|
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10 2009 002 816 |
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Current U.S.
Class: |
250/363.01;
250/367 |
Current CPC
Class: |
G01F
23/2885 (20130101); G01F 23/288 (20130101) |
Current International
Class: |
G01F
23/284 (20060101) |
Field of
Search: |
;250/361R,362,363.01,367,368,369,458.1,459.1 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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1068494 |
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Jan 2001 |
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EP |
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09080156 |
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Mar 1997 |
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JP |
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2009031074 |
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Mar 2009 |
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WO |
|
Other References
Von Dipl.-ing. Alecsandru Nistor, "Moderne Radiometrische
Fullstandmesstechnik", Messen. Prufen, Automatisieren, 1988, No.
10, Germany. cited by applicant.
|
Primary Examiner: Gaworecki; Mark R
Attorney, Agent or Firm: Bacon & Thomas, PLLC
Claims
The invention claimed is:
1. A radiometric measuring device for measuring a physical,
measured variable, of a fill substance located in a container,
and/or for monitoring an exceeding or subceeding of a predetermined
limit value for the physical, measured variable, comprising: a
radioactive radiator, which is mounted on the exterior on the
container and, during operation, sends radioactive radiation
through the container; and a detector, which is mounted on the
exterior on the container and is arranged on a side of the
container lying opposite said radiator and serves to receive a
radiation intensity penetrating through the container, dependent on
the physical, measured variable, and to convert such into an
electrical output signal, said detector having: a carrier, on which
at least one scintillation fiber is wound, which converts
radiometric radiation impinging thereon into light flashes, whose
light propagates in said respective scintillation fiber toward its
ends; at least one array of avalanche photodiodes operated in
Geiger mode for converting light impinging thereon into an
electrical signal, wherein at least one end of each of said
scintillation fiber is connected to an avalanche photodiodes of one
of the arrays; and a measuring device electronics connected to said
avalanche photodiodes, which, based on the electrical signals of
said avalanche photodiodes, produces the electrical output
signal.
2. The radiometric measuring device as claimed in claim 1, wherein:
ends of said scintillation fibers connected to said at least one
array each have a cross sectional area, which covers a plurality of
said avalanche photodiodes.
3. The radiometric measuring device as claimed in claim 1, wherein:
all said avalanche photodiodes connected to an end of a respective
one of said scintillation fiber are connected electrically in
parallel.
4. The radiometric measuring device as claimed in claim 1, wherein:
all said avalanche photodiodes of an array are connected
electrically in parallel.
5. The radiometric measuring device as claimed in claim 1, wherein:
all said arrays or said arrays and said measuring device
electronics are arranged internally of said carrier.
6. The radiometric measuring device as claimed in claim 1, wherein:
said array and said measuring device electronics are arranged in an
explosion protected housing arranged outside of said carrier; and
said ends of said scintillation fibers connected to said array are
led into said housing via an explosion-protected feedthrough.
7. The radiometric measuring device as claimed in claim 1, wherein:
along said carrier a plurality of said scintillation fibers are
wound, each of which surrounds a section of said carrier.
8. The radiometric measuring device as claimed in claim 1, wherein:
at least one of said scintillation fibers has at least one region
along a longitudinal axis of said carrier with a higher winding
density instead of a determined, constant winding density across
the registered measuring range.
9. The radiometric measuring device as claimed in claim 1, wherein:
one or more of said scintillation fibers are wound on top of one
another in two or more winding layers.
10. The radiometric measuring device as claimed in claim 1,
wherein: the two ends of one or more scintillation fibers extending
parallel to one another are connected in each case to an array; and
said measuring device electronics derives a radiation intensity
profile, based on the output signals of the arrays connected to the
first ends of the scintillation fibers, and on the output signals
of the arrays connected to the second ends of the scintillation
fibers, which profile shows a radiation intensity impinging on the
scintillation fibers as a function of location along the
scintillation fibers.
11. The radiometric measuring device as claimed in claim 1,
wherein: said measuring device electronics continuously determines,
based on the output signals of the arrays connected to the first
ends and the arrays connected to the second ends, travel time
differences between the two signal travel times, which light from a
light flash triggered in a scintillation fiber requires for the two
different travel distances from the location of origination of the
light flash to the respective ends; said measuring device
electronics registers a frequency distribution, which gives the
frequency with which the travel time differences occur; and
therefrom, said measuring device electronics determines the
radiation intensity profile, which gives the radiation intensity,
which the locations along the scintillation fibers associated with
the travel time differences are exposed to.
12. The radiometric measuring device as claimed in claim 1,
wherein: said scintillation fibers attenuates, dependent on the
length of the respective travel distance, the light of the light
flash triggered in the scintillation fibers by radiometric
radiation experiences on the two different travel distances from
the location of origination of the light flash to the respective
ends wherein said attenuation is reflected in the amplitude of the
output signals of the arrays connected to the scintillation fibers;
said measuring device electronics continuously forms the amplitude
ratios between the amplitudes of the output signals of the arrays
connected to the first ends and the amplitudes of the output
signals the arrays connected to the second ends; said measuring
device electronics registering frequency distribution, which gives
the frequency with which the amplitude ratios occur; and therefrom,
said measuring device electronics determines a radiation intensity
profile, which gives the radiation intensity, which the locations
along the scintillation fibers associated with the amplitude ratios
are exposed to.
13. The radiometric measuring device as claimed in claim 1,
wherein: the physical, measured variable is a fill level or a
density of a fill substance located in a container.
Description
TECHNICAL FIELD
The invention relates to a radiometric measuring device, which
serves to measure a physical, measured variable, especially a fill
level or a density, of a fill substance located in a container, or
to monitor a exceeding or subceeding (or falling beneath) of a
predetermined limit value for the physical, measured variable.
BACKGROUND DISCUSSION
Radioactive measuring devices include radioactive radiators, which,
during operation, send out radioactive radiation through the
container, and include detectors, which serve to detect a radiation
intensity penetrating through the container, which is dependent on
the physical, measured variable to be measured, and to convert this
into an electrical output signal. Radiometric measuring devices are
typically always applied when conventional measuring devices are
not applicable due to especially rough conditions at the measuring
location. Very frequently, extremely high temperatures and
pressures reign, for example, at the measuring location, or highly
chemically and/or mechanically aggressive environmental influences
are present, which make the use of other measuring methods
impossible.
In radiometric measurements technology, a radioactive radiator,
e.g. a Co 60 or Cs 137 preparation, is installed in a radiation
protection container, and placed at a measuring location, e.g. a
container filled with a fill substance. Such a container can be,
for example, a tank, a pipe, a conveyor belt, or any other form of
container.
The radiation protection container has a window, through which the
radiation emitted by the radiator positioned for measuring is
radiated through a wall of the radiation protection container.
Usually, a radiation direction is selected, in the case of which
the radiation penetrates that region of the container, which should
be metrologically registered. On the oppositely lying side, the
radiation intensity emerging from the container over a region to be
metrologically registered (this intensity being dependent on the
fill level or on the density of the fill substance) is
quantitatively registered with a detector. The emerging radiation
intensity depends on geometric arrangement and absorption. The
latter of these is, in the case of fill level measurement and in
the case of monitoring an exceeding or subceeding of a
predetermined fill level, dependent on the amount of fill substance
in the container, and in the case of density measurement, on the
density of the fill substance. As a result, the emerging radiation
intensity is a measure for the current fill level, the superseding
or subceeding of the predetermined fill level, or the current
density of the fill substance in the container.
Today, usually scintillation detectors having a scintillator, e.g.
a scintillation rod, and a light receiver, e.g. a photomultiplier,
are used as detector. The scintillation rod is composed of a
special plastic, e.g. polystyrene (PS) or polyvinyl toluene (PVT),
which is very optically pure. Gamma radiation triggers light
flashes in the scintillation material, whose light is registered by
the photomultiplier and converted into electrical pulses. Connected
to the photomultiplier is a measuring device electronics, which,
based on the electrical pulses, determines a pulse rate with which
the pulses occur. The pulse rate is dependent on the radiation
intensity, and is thus a measure for the physical variable to be
measured.
Solid scintillation rods have, however, the disadvantage that, due
to their dimensions, they cannot at all or can only very poorly be
connected to light receivers which today are obtainable in very
small forms of construction, since, in such case, a large part of
the light would radiate unused past the light receiver.
Correspondingly, such scintillation rods are usually used in
connection with large and expensive photomultipliers.
Added to this is the fact that, in the case of solid scintillation
rods, due to manufacturing-related surface defects, a portion of
the light escapes laterally from the rod, and is therewith lost for
metrological registration.
Detectors are known, in the case of which, instead of solid
scintillation rods, scintillating fibers are applied. Scintillation
fibers have, as a rule, a diameter in the order of magnitude of 1
mm, or in the case of fibers with a polygonal cross section, a
cross sectional area in the order of magnitude of 1 mm.sup.2, and
can accordingly be connected very well to small light
receivers.
In JP 09 080156 A, a radiometric measuring arrangement is
described, which serves to measure a radiation dose emerging from a
radioactive fill substance located in a container. For this, a
detector is used, which has a helical scintillation fiber wound
around the container, on whose two ends a light receiver, here a
photomultiplier or an avalanche photo diode, is, in each case,
connected. Radiometric radiation emerging from the fill substance
produces light flashes at locations along the fiber impinged upon
by the radiation, with these light flashes propagating toward the
two ends of the scintillation fiber. Connected to the two light
receivers is a signal processing unit, which determines a travel
time difference of the received signals attributable to one and the
same light flash, and, based on the propagation velocity of the
light signals in the fiber, determines therefrom the location of
origination of the associated light flash.
This arrangement is, however, in the described form only useable in
connection with radioactive fill substances, since the fiber
surrounds the container on all sides. In connection with the above
named measuring arrangement, in the case of which a radiation
source arranged outside of the container is used, this arrangement
would essentially metrologically register the radiative power of
the source. Moreover, the length of the scintillation fiber is
limited, since the light is attenuated in the fiber.
Correspondingly, the arrangement is only useable in connection with
relatively small containers.
In comparison to a solid scintillation rod, an individual
scintillation fiber has the disadvantage that it has a considerably
smaller irradiated mass. Accordingly, the radiative power that
impinges on an individual scintillation fiber is, in comparison,
very small.
This low irradiated mass can, for example, be compensated by the
measuring arrangement described in EP 1 068 494 B1, wherein a
detector is used, in which a number of scintillation fibers are
combined to form a bundle, whose diameter is greater than the
diameter of the individual fibers. The entire bundle is connected
at one end to a photomultiplier, which converts the light conveyed
over the scintillation fibers into an electrical signal.
Due to an irradiated mass of in the fiber bundle which is increased
in comparison to an individual fiber, the radiative power received
by the detector is increased. However, a large, expensive
photomultiplier is still made use of here. Due to the attenuation
of the scintillation light in the fibers, the length of the bundle
is limited. Moreover, fiber bundles are relatively rigid and
inflexible. Through this, the region metrologically registerable
with the scintillation fiber bundle, is constrained.
SUMMARY OF THE INVENTION
An object of the invention is to provide a radiometric measuring
device for measuring a physical, measured variable--especially a
fill level or a density--of a fill substance located in a
container, or for monitoring an exceeding or subceeding of a
predetermined limit value for the physical, measured variable, with
a radioactive radiator, which, during operation, sends radioactive
radiation through the container, and with a detector having at
least one scintillator and at least one light receiver connected
thereto, which detects a radiation intensity penetrating through
the container, dependent on the physical, measured variable to be
measured; wherein, with this measuring device, in an extremely
flexible predeterminable region to be metrologically registered by
the detector, a very precise measuring of the radiation intensity
can be performed.
For this, the invention resides in a radiometric measuring device
for measuring a physical, measured variable--especially a fill
level or a density--of a fill substance located in a container,
and/or for monitoring an exceeding or subceeding of a predetermined
limit value for the physical, measured variable, comprising: A
radioactive radiator, which, during operation, sends radioactive
radiation through the container; and a detector, which is arranged
on a side of the container lying opposite the radiator and serves
to receive a radiation intensity penetrating through the container,
dependent on the physical, measured variable, and to convert such
into an electrical output signal, wherein the detector has a
carrier, on which at least one scintillation fiber is wound, which
converts radiometric radiation impinging thereon into light
flashes, whose light propagates in the respective scintillation
fiber toward its ends, and includes at least one array (13, 13') of
avalanche photodiodes (APD) operated in the Geiger mode for
converting light impinging thereon into an electrical signal,
wherein at least one end (E1, E2) of each scintillation fiber (11)
is connected to avalanche photodiodes of one of the arrays (13,
13'), and wherein the detector has a measuring device electronics
(23) connected to the avalanche photodiodes (APD), which, based on
the electrical signals of the avalanche photodiodes (APD), produces
the electrical output signal.
In a preferred embodiment, the ends of the scintillation fibers
connected to the arrays have a cross sectional area, which covers a
plurality of avalanche photodiodes.
In an additional embodiment, all avalanche photodiodes connected to
one end of a scintillation fiber are connected electrically in
parallel.
In an additional embodiment, all avalanche photodiodes of an array
are connected electrically in parallel.
In a further development, all arrays or the arrays and the
measuring device electronics are arranged in the interior of the
carrier.
In another further development the arrays and the measuring device
electronics are arranged in an explosion-protected housing arranged
outside of the carrier, and the ends of the scintillation fibers
connected to the arrays are led into the housing via an
explosion-protected feedthrough.
In an additional further development, wound along the carrier are a
plurality of scintillation fibers, each of which surrounds a
section of the carrier.
In another further development, at least one of the scintillation
fibers has along a longitudinal axis of the carrier at least one
region with a higher winding density.
In an additional further development, one or more scintillation
fibers are wound in two or more winding layers on top of one
another.
Additionally, the invention includes a method for operation of a
measuring device of the invention, in the case of which the two
ends of one or more scintillation fibers extending parallel to one
another are in each case connected to an array, and the measuring
device electronics, based on the output signals of the array
connected to the first ends of the scintillation fibers and the
output signals of the array connected to the second ends of the
scintillation fibers, derives a radiation intensity profile, which
shows radiation intensity on the scintillation fibers as a function
of location along the scintillation fibers.
It likewise includes an embodiment of this method, wherein based on
the output signals of the arrays connected to the first ends and
the arrays connected to the second ends, travel time differences
between the two signal travel times are continuously determined,
which light from a light flash triggered in a scintillation fiber
requires for the two different travel distances from the location
of origination of the light flash to the respective ends, a
frequency distribution is registered, which gives the frequency
with which the travel time differences occur, and therefrom, the
radiation intensity profile is determined, which gives the
radiation intensity, which the locations along the scintillation
fibers associated with the travel time differences are exposed
to.
Alternatively, it includes a further development of this method, in
the case of which light of the light flash triggered in the
scintillation fibers by radiometric radiation experiences on the
two different travel distances from the location of origination of
the light flash to the respective ends an attenuation dependent on
the length of the respective travel distance, which is reflected in
the amplitude of the output signals of the arrays connected to the
scintillation fibers, the amplitude ratios between the amplitudes
of the output signals of the arrays connected to the first ends and
the amplitudes of the output signals of the arrays connected to the
second ends are continually formed, a frequency distribution is
registered, which gives the frequency with which the amplitude
ratios occur, and therefrom, a radiation intensity profile is
determined, which gives the radiation intensity, which the
locations along the scintillation fibers associated with the
amplitude ratios are exposed to.
The invention has the advantage that the irradiated mass of wound
scintillation fibers is markedly higher than the irradiated mass of
fibers which extend outward. Additionally, the amount of light in
the scintillation fibers occurring due to radiation is measurable
by the APDs operated in the Geiger mode extremely precisely and
practically without losses.
A further advantage lies in the fact that, due to the APDs operated
in the Geiger mode, a plurality of scintillation fibers can be
used, which can be arranged in parallel or in a plurality of
winding layers on top of one another, and that individual
scintillation fibers or a plurality of scintillation fibers can be
arranged on top of one another along the region to be
metrologically registered in individual zones, in that the APDs
connected thereto or the totality of the arrays are operated in
parallel.
A further advantage lies in the fact that not only the radiation
intensity as a whole, but, by means of APDs connected to both ends
the scintillation fibers, also very detailed radiation intensity
profiles along the region metrologically registered by the detector
can be created. In such case, an extremely high locational
resolution is achievable with the wound scintillation fibers.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention and other advantages will now be explained in greater
detail on the basis of the figures of appended drawing, in which
five examples of embodiments are presented; in the figures, equal
parts are provided with equal reference characters. The figures of
the drawing show as follows:
FIG. 1 is a radiometric measuring arrangement;
FIG. 2 is an array of avalanche photodiodes with a scintillation
fiber end connected thereto;
FIG. 3 is an array of avalanche photodiodes with nine scintillation
fiber ends connected thereto;
FIG. 4 is a circuit diagram with avalanche photodiodes connected
electrically in parallel and operated in the Geiger mode;
FIG. 5 is a detector with an explosion-protected housing for
accommodating the array and the measuring device electronics;
FIG. 6 is a measuring arrangement for registering a radiation
intensity profile;
FIG. 7 is a carrier with a scintillation fiber wound thereon, which
has a region with a higher winding density;
FIG. 8 is a carrier, on which scintillation fibers are applied in a
plurality of winding layers;
FIG. 9 is a scintillation fiber wound on a planar plate; and
FIG. 10 is a carrier, which has individual portions on which, in
each case, a scintillation fiber is wound.
DETAILED DISCUSSION IN CONJUNCTION WITH THE DRAWINGS
FIG. 1 shows a sketch of the principles of a measuring arrangement
having a radiometric measuring device of the invention for
measuring a physical, measured variable--especially a fill level or
a density--of a fill substance located in a container and/or for
monitoring an exceeding or subceeding of a predetermined limit
value for the physical, measured variable.
The measuring arrangement includes a container 3 fillable with a
fill substance 1, and a radioactive radiator 5 mounted on the
exterior on the container 3, which, in measurement operation, sends
radioactive radiation through the container 3. The radiator 5
includes a radiation protective container, into which a radioactive
preparation, e.g. a Co 60 or Cs 137 preparation, is inserted. The
radiation protection container includes a window, through which the
radiation escapes in a radiating direction predetermined by the
orientation of the window, and irradiates the container 3. A
radiation cone forms around the radiating direction with an
aperture angle a, which irradiates a region of the container 3 to
be metrologically registered.
On a side of the container 3 lying opposite the radiator 5, a
detector 7 (here shown in section) is arranged, which serves to
receive penetrating through the container 3 over an
application-specific, predetermined region to be metrologically
registered by the detector 7 a radiation intensity dependent on the
physical, measured variable, and to convert this into an electrical
output signal.
Detector 7 includes a carrier 9 and at least one scintillation
fiber 11 wound onto the carrier 9. Scintillation fibers 11 convert
radiometric radiation impinging thereon into light flashes, whose
light propagates in both directions within the respective
scintillation fiber 11, up to its ends E1, E2. Via the winding of
the scintillation fibers 11, a marked increasing of the mass which
is radiated through is achieved. A wound scintillation fiber 11
accordingly absorbs clearly more radiative power than an individual
stretched out fiber.
At least one end E1, E2 of each scintillation fiber 11 is connected
to an array 13, 13' of avalanche photodiodes (APD) operated in the
Geiger mode. As already mentioned, due to the attenuation of the
light occurring in scintillation fibers 11, the length of
scintillation fibers 11 is limited to a predetermined maximum
length. If the two ends E1, E2 of scintillation fibers 11 are each
connected to APDs of an array 13, 13', scintillation fibers 11 up
to twice as long can then be used.
The arrays 13, 13' are very small and cost effective in comparison
to photomultipliers. They are, for example, sold by the firm
HAMAMATSU under the product designation Multi-Pixel Photon Counter.
Obtainable from such source are, for example, arrays with an active
area of 1.times.1 mm, on which 100, 400 or 1600 APDs are arranged,
and arrays 13 with an active area of 3.times.3 mm, on which 900,
3600 or 14400 APDs are arranged.
Scintillation fibers 11 are obtainable with, for example, a
diameter in the order of magnitude of 1 mm, or, in the case of
fibers with polygonal cross sections, with a cross sectional area
in the order of magnitude of 1 mm.sup.2, and are therewith
optimally suitable for connection to these arrays 13. FIG. 2 shows
a fiber end 15 with a round cross section, connected to an array
13. The fiber end 15 has a cross sectional area which covers a
plurality of APDs, here just under 100 APDs. If a plurality of
scintillation fibers 11 are used in parallel, a plurality of
scintillation fibers 11 are then preferably connected to an array
13. FIG. 3 shows nine fiber ends 17, each with a rectangular cross
section, connected to an array 13.
The APDs convert light impinging thereon into an electrical signal.
With these arrays 13, it is possible to detect extremely low
amounts of light occurring spatially distributed across the cross
sectional area of the ends E1, E2 of the scintillation fibers 11.
In such case, the APDs are preferably operated in the Geiger mode.
FIG. 4 shows a corresponding measurement circuit. There, at each
APD in the blocking direction, an equal voltage U is present which
is constant for all APDs of an array 13, and which lies above the
avalanche voltage of the diodes. In this state, even an individual
photon occurring on an APD leads to a Geiger discharge, which, as
an output current, flows over a quench resistor R connected in
series with the APD. In this way, a highly accurate measuring of
the produced light amount, and therewith the radiation intensity,
is correspondingly possible. The strength of the output current is
constant and independent of the number of photons that have led to
the discharge. The Geiger mode offers the advantage that a
plurality of APDs can be connected electrically in parallel, as is
schematically presented in FIG. 4. The output current of the
parallel circuit is then equal to the sum of the output currents of
the individual APDs in which a discharge has taken place, and is,
for example, converted via a current-voltage converter 19 into a
voltage, which is fed to a comparator circuit 21. Converter 19 and
comparator circuit 21 are preferably integrated into the array
chip, and consequently are not separately presented in the
remaining figures. At the output of the comparator circuit 21, an
output signal A is therewith available, which corresponds to the
plurality of APDs connected in parallel which, at this point in
time t, have received at least one photon. In such case, the Geiger
mode operation enables a very high measure of flexibility as
regards signal pickup and evaluation. For example, all APDs
connected to scintillation fibers 11 can be connected in parallel,
and all APDs connected to the first ends E1 and/or all APDs
connected to the second ends E2 of a plurality of parallelly
operated scintillation fibers 11 can be connected in parallel.
Likewise, two or more arrays 13, 13' can be operated in parallel.
In this way, the obtaining of the measurement signal can be
tailored in a very flexible manner to the most varied of measuring
tasks.
The output signals A are fed as output signals of the respective
array 13 to a measuring device electronics 23, which determines
therefrom a pulse rate, i.e. the number of APDs triggered per time
unit. In such case, all APDs of all arrays 13, 13' can be operated
in parallel, so that the individual output signals A of the arrays
13, 13' are added up to a sum signal. The pulse rate derived based
on this sum signal is a measure for the total light amount
occurring in all scintillation fibers 11, and is therewith a
measure for the radiation intensity impinging on the associated
scintillation fibers 11. This is, in turn, a measure for the
physical, measured variable to be measured or monitored. From this,
the measuring device electronics 23 generates an output signal
corresponding to the sought measured variable, and makes this
available to a display and/or to an additional processing unit. The
output signal is output, for example, via a current output, a
digital output or via a data bus connection.
For achieving an extremely compact form of construction of the
detectors 7 of the invention--as is presented in the examples of
embodiments illustrated in FIGS. 1, 7, 8 and 10--hollow carriers 9
are preferably applied and the array or the arrays 13, 13' are
arranged in the interior of the carrier 9. Preferably, the
measuring device electronics 23 connected to the arrays 13, 13' is
also arranged in the interior of carrier 9.
An exception to this is formed by applications in the case of which
the measuring device is used in explosive atmospheres. There, as a
rule, it is legally prescribed that electrical components which
convey energies which are sufficient to produce an ignition spark
are arranged in pressure-resistant encapsulated housings. Since the
scintillation fibers 11 themselves do not contain any electrical
components relevant for explosion protection, the scintillation
fibers 11 can be laid exposed, even in explosive atmospheres.
Consequently, in these applications, measuring devices of the
invention are preferably applied, wherein the array 13 and the
measuring device electronics 23 are arranged in an
explosion-protected housing 25, which is arranged outside of the
carrier 9, and the ends E1 of the scintillation fibers 11 connected
to the array 13 are inserted into the housing 25 via an
explosion-protected feedthrough 27. An example of this is shown in
FIG. 5.
The detectors 7 of the invention offer a high measure of
flexibility as regards the region which is irradiated by the
radiator 5 and which is to be metrologically registered by the
detector 7, and as regards the achievable measurement results.
In the variant shown in FIG. 1, the carrier 9 is a tubular spindle,
on which a scintillation fiber 11 is wound with a constant winding
density. Via the winding density, the height of the metrologically
registerable region is, in such case, adjustable within the limits
defined by the total length of the scintillation fiber 11. The
greater the winding separation, the greater is the height of the
metrologically registerable region. If only one end of the
scintillation fiber 11 is connected to an array 13 of APDs, the
latter's output signal, which is proportional to the number of
triggered APDs, is fed to the measuring device electronics 23. This
then determines, as described above, the radiation intensity
arising on the scintillation fiber 11 (which is dependent on the
measured variable) and derives the measured variable therefrom. If,
for increasing or doubling the maximum usable fiber length, the two
ends E1, E2 of the scintillation fiber 11 are in each case
connected to an array 13, 13', the output signals of the two arrays
13, 13' are fed to the measuring device electronics 23, which then,
based on the sum of the output signals, determines the radiation
intensity.
If the two ends E1, E2 of a scintillation fiber 11 are each
connected to an array 13, 13', the radiation arising on the
scintillation fiber 11 can alternatively or additionally be
associated by means of the output signals of the two arrays 13, 13'
with locations along the scintillation fiber 11, on which light
flashes occurring due to the impinging radiation are triggered. For
this, the two subsequently described methods can be applied, for
example.
A first such method based on a travel time measurement is described
in detail in DE 101 32 267 A1, and is performable with a markedly
improved accuracy of measurement with the measuring devices of the
invention. A photon absorbed at a particular location along the
scintillation fiber 11 produces a light flash, whose light, after a
first signal travel time t.sub.1 dependent on the location of
origination of the light flash, arrives at the one array 13, and
after a second signal travel time t.sub.2 dependent on the location
of origination of the light flash arrives at the other array 13'.
On the basis the output signals of the two arrays 13, 13' a travel
time difference .DELTA.t=t.sub.2-t.sub.1 between the two signal
travel times t.sub.1, t.sub.2 is determined by the measuring device
electronics 23. The travel time differences .DELTA.t become evident
due to the different travel distances of the light in the
scintillator fiber 11, which are dependent on the location of
origination. Based on the propagation velocity of the light in the
scintillation fiber 11, or based on a corresponding measuring
device calibration, these travel time differences are associated
with the location of origination along the scintillation fiber 11
The measuring device of the invention offers here the advantage
that over the height of the metrologically registered region, an
extremely exact locational resolution is achievable, since the
light in the wound scintillation fiber 11 must travel through one
complete winding length in order to pass through one winding
separation in height.
For highly accurate fill level measurement or for creation of a
density profile over the height H metrologically registered by the
scintillation fiber 11, the output signals A1, A2 of the two arrays
13, 13' are fed to measuring device electronics 23, which
continuously determines the travel time differences and derives
therefrom a frequency distribution, which gives the frequency with
which the travel time differences occur. The frequency with which a
particular travel time difference occurs gives the radiation
intensity, which the location along the scintillation fiber 11
associated with this travel time difference is exposed to.
Since the scintillation fibers 11 are very thin, extremely small
winding spacings, e.g. of a millimeter, can be implemented. In this
way, very fine density profile measurements, as well as fill-level
measurements accurate to the millimeter are for the first time
possible. These accuracies are not achievable with the measuring
device described in DE 101 32 267 A1, which uses a single solid
scintillation rod.
A second method is based on an amplitude comparison of the output
signals A1, A2 of the two arrays 13, 13' and is presented in FIG. 6
in a sketch of the principle. A photon absorbed at a particular
location h along the scintillation fiber 11 produces a light flash,
whose light on the way to the one array 13 travels a first path
dependent on the location of origination of the light flash, and on
the way to the other array 13', travels a second path dependent on
the location of origination of the light flash. On both paths, the
light experiences attenuation dependent on the length of the
particular path. This is reflected directly in the amplitudes A1,
A2 of the output signals of the two arrays 13, 13'. Triggered by a
gamma photon impinging on scintillation fiber 11 in the vicinity of
the array 13 at the height h, array 13, as shown in FIG. 6,
delivers an output signal A1 with a comparatively high amplitude
A.sub.h1, while the array 13' connected to the other end of the
scintillation fiber 11 in this case delivers an output signal A2
with a much smaller amplitude A.sub.h2. The ratio A1/A2 of the
amplitudes of the two output signals is dependent on the location
of origination of the light flash. The ratio A1/A2 becomes larger
the closer the array 13 is to the location of origination, because
amplitude A1 is in the numerator of the ratio. The ratio can
accordingly be directly taken into consideration as a measure for
the height along the region metrologically registered by the
scintillation fiber 11. For highly accurate fill level measurement
or for creation of a density profile over the height H
metrologically registered by the scintillation fiber 11, the output
signals A1, A2 are fed to the measuring device electronics 23,
which continuingly forms the ratios of the amplitudes of the output
signals, and derives therefrom a frequency distribution, which
gives the frequency # with which the amplitude ratios A1/A2 occur.
This can, as shown in FIG. 6 in the function block 23 of the
measuring device electronics, occur in the form of a histogram. The
frequency with which a particular amplitude ratio occurs gives the
radiation intensity, which the location along the scintillation
fiber 11 associated with the amplitude ratio is exposed to.
Both methods can naturally be performed not only with a single
scintillation fiber 11, but also in a completely analogous manner
with a plurality of scintillation fibers 11 run parallel to one
another. In such case, the Geiger mode offers the advantage that
all APDs connected to the first ends E1 of these scintillation
fibers 11 are either directly connected electrically in parallel,
or the associated arrays 13 are operated in parallel, in that the
output signals of these array 13 can be added up to a sum signal.
The same is naturally true for the second ends E2 of these
scintillation fibers 11.
Instead of a constant winding density across the registered
measuring range, detectors 7 can also be implemented, wherein at
least one of the scintillation fibers 11 has at least one region 29
with a higher winding density along the longitudinal axis of the
carrier 9. This variant is shown in FIG. 7. It is especially
advantageous in connection with the two earlier described
locational resolving methods, since here, via the regions 29 with a
higher winding density, zones can be targetedly predetermined or
selected, in which a higher locational resolution of the impinging
radiation intensity is desired. These can be, for example in the
context of a fill level measurement, zones in which an exceeding or
subceeding of a predetermined fill level should be highly
accurately monitored. Likewise, they can be for density
measurements, in the case of which an especially detailed density
profile should be created in individual zones, e.g. in zones, in
which interfaces can form between individual fill substance
layers.
FIG. 8 shows a section through another variant, wherein for
increasing the irradiated mass, scintillation fibers 11a, 11b, 11c
are wound on top of one another in two or more winding layer 31,
33, 35. In such case, depending on the height of the region to be
metrologically registered, a single scintillation fiber 11 can be
wound in multiple layers, or--as presented here--a separate
scintillation fiber 11a, 11b, 11c can be used for each winding
layer 31, 33, 35. If a plurality of scintillation fibers 11 are
used, these can be connected in parallel relative to one another to
one or more arrays 13 with APDs operated in the Geiger mode.
For increasing the cross sectional area of the metrologically
registered region, areal shapes--such as, for example, plates 37
which are planar or warped in imitation of the container
geometry--on which one or more scintillation fibers 11 are wound in
one or more layers can also be used as carrier 9. This variant is
shown in FIG. 9. As plates 37, planar or warped circuit boards, for
example, which preferably are laterally provided with grooves 39
for accommodating the scintillation fibers 11, are suitable.
In order to enlarge the height of the metrologically registered
region, along a correspondingly long support 9, a plurality of
scintillation fibers 11 can also be wound on top of one another on
carrier 9, wherein the fibers in each case surround a section 41 of
carrier 9. This variant is shown in FIG. 10 and is used, for
example, to measure fill levels in very high containers 3. In order
to achieve here a homogeneous covering of the entire height to be
metrologically registered, the portions 41 border directly on one
another. Alternatively, the individual sections 41 can also
naturally be arranged at selected heights along the support 9, e.g.
at heights, which lie in the region of predetermined fill levels,
whose exceeding or subceeding should be monitored. Also here,
instead of the illustrated individual scintillation fibers 11, in
each section 41, a plurality of winding layers of one or more
scintillation fibers 11 can naturally be provided on top of one
another, as is presented in FIG. 8.
Also here, either an end E1 or the two ends E1 and E2 of each
scintillation fiber 11a, 11b, 11c can in each case be connected to
an array 13. The measuring can then be performed in various
manners, depending on application and desired accuracy of
measurement and resolution. In the simplest case, all of the APDs
are operated in parallel; all APDs of each array 13, 13' are
connected electrically in parallel, and the output signals A of all
arrays 13, 13' are combined in the measuring device electronics 23
to a sum signal, and therefrom, the total radiative power recorded
by the detector is determined. Alternatively, the radiative power
can be individually determined for each region.
If the two ends E1, E2 of the scintillation fibers 11a, 11b, 11c
are, in each case, connected to an array 13, 13', a locationally
dependent radiation profile can then naturally also be derived here
based on the two methods described above, which gives the radiative
power as a function of the location versus the height of the
detector 7 covered by individual portions 41 or all portions
41.
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